Near-Cathode Plasma Layer on CuCr Contacts of Vacuum Arcs

Almeida, N. A.; Benilov, M. S.; Benilova, Larissa G.; Hartmann, Werner; Wenzel, N.

doi:10.1109/tps.2013.2260832

Cited by 39 publications

(74 citation statements)

References 58 publications

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“…Note that a characteristic feature of nearcathode layers in vacuum arcs is the ionization of evaporated metal atoms occurring primarily in the outer section of the near-cathode space-charge sheath, rather than in the quasineutral plasma (ionization layer) as in the case of nonemitting cathodes discussed in Section II-A. This feature is reflected in the model [20], which comprises a self-consistent description of the space-charge sheath with ionization of evaporated atoms and with a maximum of potential occurring inside the sheath. Also considered is balance of the evaporated metal atoms with their eventual return to the cathode if ionized before the potential maximum, as well as balance of the electron energy.…”

Section: Chromium Cathodementioning

confidence: 98%

“…Therefore, balance of electron energy in the near-cathode layer may be evaluated and the local electron temperature found independently of the bulk plasma. This is the approach employed in models of near-cathode layers in arc discharges both in ambient gases and vacuum (see [17] and references therein and [18]- [20], respectively). In addition to the ion current, such models compute also the electron emission current with account of Schottky correction or thermo-field emission mechanism and the current of plasma electrons reaching the cathode against the retarding electric field in the space-charge sheath.…”

Section: B Emitting Cathodesmentioning

confidence: 99%

“…As discussed in Section II-B, one can perform a self-consistent evaluation by means of a relevant model of near-cathode layers in arc discharges in this case. In this paper, the model of near-cathode layers in vacuum arcs [20] is used. Note that a characteristic feature of nearcathode layers in vacuum arcs is the ionization of evaporated metal atoms occurring primarily in the outer section of the near-cathode space-charge sheath, rather than in the quasineutral plasma (ionization layer) as in the case of nonemitting cathodes discussed in Section II-A.…”

Section: Chromium Cathodementioning

confidence: 99%

See 2 more Smart Citations

Physics of Spotless Mode of Current Transfer to Cathodes of Metal Vapor Arcs

Benilov

Benilova

2015

IEEE Trans. Plasma Sci.

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A fresh attempt is made to clarify the physics of the diffuse, or spotless, mode of current transfer that may occur on cathodes of vacuum arcs if the average cathode surface temperature is high enough, about 2000 K. It is shown that in the case of chromium cathode the usual mechanism of current transfer to arc cathodes cannot sustain current densities of the order of 10 5 -10 6 A · m −2 observed in the experiment, the reason being that the electrical power deposited into electron gas in the nearcathode space-charge sheath is insufficient. It is hypothesized that the electrical power is supplied to the electron gas primarily in the bulk plasma, rather than in the sheath, and a high level of electron energy in the vicinity of the sheath edge is sustained by electron heat conduction from the bulk plasma. Estimates of the current of ions diffusing to the sheath edge from the quasineutral plasma gave values comparable with the experimental current density, which supports the above hypothesis. On the contrary, the spotless attachment of vacuum arcs to gadolinium cathodes may be interpreted as a manifestation of the usual mechanism of current transfer to arc cathodes. Results given for gadolinium cathodes by a model of near-cathode layers in vacuum arcs conform to available experimental information.

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Section: Chromium Cathodementioning

confidence: 98%

Section: B Emitting Cathodesmentioning

confidence: 99%

Section: Chromium Cathodementioning

confidence: 99%

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Physics of Spotless Mode of Current Transfer to Cathodes of Metal Vapor Arcs

Benilov

Benilova

2015

IEEE Trans. Plasma Sci.

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“…2-D numerical modeling of vacuum arc spots is reported in [5]- [14]. In particular, in [12] and [13] cathode spots on composite CuCr contacts have been studied in the case where chromium grains are large, which occurs at initial stages of life of contacts of highpower circuit breakers. It was found that in this case spots with currents of the order of tens of amperes operating on the copper matrix coexist with spots with currents of the order of one or few amperes on chromium grains.…”

mentioning

confidence: 99%

“…It was found that in this case spots with currents of the order of tens of amperes operating on the copper matrix coexist with spots with currents of the order of one or few amperes on chromium grains. This paper represents a continuation of [12] and [13] and is concerned with simulation of spots attached to Cr grains in the Cu matrix in a wide range of values of the ratio of the grain radius to the radius of the spot. Also studied is the stability of stationary spots as well as the sensitivity of the obtained results with respect to variations in different aspects of the simulation model.…”

mentioning

confidence: 99%

Modeling Spots on Composite Copper–Chromium Contacts of Vacuum Arcs and their Stability

Benilov

Cunha

Hartmann

et al. 2015

IEEE Trans. Plasma Sci.

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Cathode spots on copper-chromium contacts of vacuum interrupters are simulated by means of a self-consistent space-resolved numerical model of cathode spots in vacuum arcs developed on the basis of the COMSOL Multiphysics software. Attention is focused on spots attached to Cr grains in the Cu matrix in a wide range of values of the ratio of the grain radius to the radius of the spot. In the case where this ratio is close to unity, parameters of spot are strongly different from those operating on both pure-copper and pure-chromium cathodes; in particular, the spot is maintained by Joule heat generation in the cathode body and the net energy flux is directed from the cathode to the plasma and not the other way round. An investigation of stability has shown that stationary spots are stable if current controlled. However, under conditions of highpower circuit breakers, where the near-cathode voltage is not affected by ignition or extinction of separate spots, the spots are unstable and end up either in explosive-like behavior or in destruction by thermal conduction. On the other hand, spots live significantly longer-up to one order of magnitude-if the spot and grain sizes are close; else, typical spot lifetimes are of the order of 10 µs. This result is very interesting theoretically and may explain the changes in grain size occurring in the beginning of the lifetime of contacts of high-power current breakers. A sensitivity study has shown that variations in different aspects of the simulation model produce quantitative changes but do not affect the results qualitatively.

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Element- and charge-state-resolved ion energies in the cathodic arc plasma from composite AlCr cathodes in argon, nitrogen and oxygen atmospheres

Franz

Polcik

Anders

2015

Surface and Coatings Technology

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The energy distribution functions of ions in the cathodic arc plasma using composite AlCr cathodes were measured as a function of the background gas pressure in the range 0.5 to 3.5 Pa for different cathode compositions and gas atmospheres. The most abundant aluminium ions were Al+ regardless of the background gas species, whereas Cr2+ ions were dominating in Ar and N2 and Cr+ in O2 atmospheres. The energy distributions of the aluminium and chromium ions typically consisted of a high-energy fraction due to acceleration in the expanding plasma plume from the cathode spot and thermalised ions that were subjected to collisions in the plasma cloud. The fraction of the latter increased with increasing background gas pressure. Atomic nitrogen and oxygen ions showed similar energy distributions as the aluminium and chromium ions, whereas the argon and molecular nitrogen and oxygen ions were formed at greater distance from the cathode spot and thus less subject to accelerating gradients. In addition to the positively charged metal and gas ions, negatively charged oxygen and oxygen-containing ions were observed in O2 atmosphere. The obtained results are intended to provide a comprehensive overview of the ion energies and charge states in the arc plasma of AlCr composite cathodes in different gas atmospheres as such plasmas are frequently used to deposit thin films and coatings.

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Near-Cathode Plasma Layer on CuCr Contacts of Vacuum Arcs

Cited by 39 publications

References 58 publications

Physics of Spotless Mode of Current Transfer to Cathodes of Metal Vapor Arcs

Physics of Spotless Mode of Current Transfer to Cathodes of Metal Vapor Arcs

Modeling Spots on Composite Copper–Chromium Contacts of Vacuum Arcs and their Stability

Element- and charge-state-resolved ion energies in the cathodic arc plasma from composite AlCr cathodes in argon, nitrogen and oxygen atmospheres

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